Niacin causes sudden release of histamine which produces certain s/e which are not seen with nicotinamide

Intense flushing

Tingling

Numbness

Throbbing headache due to cerebral vasodilation.

Q. 2

A 54-year-old man has a total cholesterol of 272 and LDL level of 210. His therapy is initiated with dietary modification and an exercise regimen, but he is unresponsive and so is prescribed nicotinic acid (Niacin). Which of the following symptoms will this patient likely experience from this drug?

A

Bradycardia

B

Facial flushing

C

Hypoalbuminemia

D

Hypoglycemia

Q. 2

A 54-year-old man has a total cholesterol of 272 and LDL level of 210. His therapy is initiated with dietary modification and an exercise regimen, but he is unresponsive and so is prescribed nicotinic acid (Niacin). Which of the following symptoms will this patient likely experience from this drug?

A

Bradycardia

B

Facial flushing

C

Hypoalbuminemia

D

Hypoglycemia

Ans.

B

Explanation:

Niacin, or vitamin B3, is an agent that results in the following physiologic changes: LDL reductions tend to occur in 5-7 days with the maximal effect seen in 3-5 weeks; triglycerides and VLDL are reduced by 20% to 40% in 1-4 days; and HDL levels can increase by 20%.

This agent is indicated as adjunctive therapy in patients with elevated cholesterol and triglycerides when diet and other nondrug therapies are inadequate.

The most common adverse effect of this agent is generalized flushing with a sensation of warmth, especially in the facial area.

This reaction may be so severe in some patients that they discontinue therapy.

Maize contains the vitamin niacin. Pellagra is a disease that results from niacin deficiency.

Assertion: Consumption of maize may aggravate Pellagra.

Reason: Some strains of maize contains excess of Leucine which interferes in the conversion of Tryptophan into Niacin.

A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

C

Assertion is true, but Reason is false

D

Assertion is false, but Reason is true

Q. 3

Maize contains the vitamin niacin. Pellagra is a disease that results from niacin deficiency.

Assertion: Consumption of maize may aggravate Pellagra.

Reason: Some strains of maize contains excess of Leucine which interferes in the conversion of Tryptophan into Niacin.

A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

C

Assertion is true, but Reason is false

D

Assertion is false, but Reason is true

Ans.

A

Explanation:

Pellagra is caused by Niacin deficiency and anything that interferes in the absorption or production of Niacin will aggravate the condition.

Ref: Park’s Textbook of Preventive Medicine, 17th Edition, Page 427.

Q. 4

A 10 year old child is suspected of having pellagra because of chronic symptoms including diarrhea, a red scaly rash, and mild cerebellar ataxia. However, his diet is not deficient in protein and he appears to be ingesting adequate amounts of niacin. A sister has a similar problem. Chemical analysis of his urine demonstrates large amounts of free amino acids. Which of the following is the most likely diagnosis?

A

Alkaptonuria

B

Carcinoid syndrome

C

Ehlers-Danlos syndrome

D

Hartnup’s disease

Q. 4

A 10 year old child is suspected of having pellagra because of chronic symptoms including diarrhea, a red scaly rash, and mild cerebellar ataxia. However, his diet is not deficient in protein and he appears to be ingesting adequate amounts of niacin. A sister has a similar problem. Chemical analysis of his urine demonstrates large amounts of free amino acids. Which of the following is the most likely diagnosis?

A

Alkaptonuria

B

Carcinoid syndrome

C

Ehlers-Danlos syndrome

D

Hartnup’s disease

Ans.

D

Explanation:

The child has Hartnup’s disease.

This condition clinically resembles pellagra (“diarrhea, dementia, and dermatitis”), and may be misdiagnosed as this nutritional (niacin) deficiency. In fact, niacin therapy may actually be helpful in controlling the symptoms.

The underlying problem is a defect in the epithelial transport of neutral amino acids, including tryptophan, which can act as a precursor of niacin. The defective amino acid transport leads to poor absorption of dietary amino acids as well as excess amino acid secretion in the urine.

Alkaptonuria is characterized by urine that turns black upon standing and a debilitating arthritis.

Carcinoid syndrome is seen in patients with carcinoid tumor. It is characterized by episodes of flushing, diarrhea, hypertension, and bronchoconstriction.

Ehlers-Danlos syndrome is a disease characterized by abnormal collagen formation leading to very elastic skin, joint problems, and fragility of some blood vessels and the intestines.

Triacylglycerol or triglyceride is an ester that is derived from glycerol and three fatty acids. Chylomicrons are lipoproteins that are lowest in density and largest in size which contains the highest percentage of triacylglycerol and the smallest percentage of protein.

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Glycolipids

Q. 1 Glycerol is the backbone of all of the following phospholipids EXCEPT

A

Phosphatidylethanolamine

B

Cardiolipin

C

Phosphatidylcholine

D

Sphingomyelin

Q. 1 Glycerol is the backbone of all of the following phospholipids EXCEPT

A

Phosphatidylethanolamine

B

Cardiolipin

C

Phosphatidylcholine

D

Sphingomyelin

Ans.

D

Explanation:

Sphingomyelin = phosphorylcholine + ceramide

Ceramide = fatty acid + sphingosine

Sphingosine = condensing palmitic acid with a decarboxylated serine and then reducing the product

Glycerol never is involved in the structure of sphingomyelin. Phosphatidylethanolamine, cardiolipin, phosphatidylcholine, and phosphatidylinositol are synthesized using phosphatidic acid as the basic building block Phosphatic acid is diacylglycerol with a phosphate ester on carbon three; therefore, glycerol is the backbone of all of these compounds. FAQ Sphingomyelin :-

– Membranous myelin sheath that surrounds nerve cell axons.

– It is the only sphingolipid NOT derived from Glycerol.

– Associated with increased accumulation in Niemann-Pick Disease.

Q. 2

Which of the following occurs in the lipidosis known as Tay-Sachs disease?

A

Synthesis of a specific ganglioside is excessive

B

Xanthomas due to cholesterol deposition are observed

C

Phosphoglycerides accumulate in the brain

D

Ganglioside GM2 is not catabolized by lysosomal enzymes

Q. 2

Which of the following occurs in the lipidosis known as Tay-Sachs disease?

A

Synthesis of a specific ganglioside is excessive

B

Xanthomas due to cholesterol deposition are observed

C

Phosphoglycerides accumulate in the brain

D

Ganglioside GM2 is not catabolized by lysosomal enzymes

Ans.

D

Explanation:

In the genetic disorder known as Tay-Sachs disease, ganglioside GM2 is not catabolized. As a consequence, the ganglioside concentration is elevated many times higher than normal. The functionally absent lysosomal enzyme is β-N- acetylhexosaminidase.

The elevated GM2 results in irreversible brain damage to infants, who usually die before the age of 3 years. Under normal conditions, this enzyme cleaves N- acetylgalactosamine from the oligosaccharide chain of this complex sphingolipid, allowing further catabolism to occur.

The cause of most lipidoses (lipid storage diseases) is similar.

That is, a defect in catabolism of gangliosides causes abnormal accumulation.

– Glyco-sphingolipid is made up of ceramide (which is a long chain fatty acid attached to amino group of sphingosine through an amide linkage i.e. = sphingosine/ amino alcohol + Fatty acid) attached directly to mono /oligo saccharide

(polar head) by an 0-glycosidic bond. Glycosphingolipids differ from sphingomyelin (phospho- sphingolipid) in that they do not contain phosphate (polar group); and differ from glycerophospholipids (phosphoglycerides) that they do not contain glycerol.

Isoenzymes are the multiple forms of the same enzyme in a single species that catalyze the same chemical reaction or reactions, but differ from each other structurally, electrophoretically and immunologically.

Though the same chemical reaction is catalyzed, the different isoenzymes may catalyze the same reaction at different rates.

Isoenzymes have different pH optimes, Km and V max values.

Isoenzymes may differ in their amino acid sequence and their quarternary structures.

The isoenzymes may have different properties also for e.g. LDH-4 and LDH-5 are easily destroyed by heat, whereas LDH-1 and LDH-2 are not, if heated upto 60°C. (Heat resistant).

Individual isoenzymes (isozymes) are distinguished and numbered on the basis of electrophoretic mobility, with the number 1 being assigned to that form having the highest mobility toward the anode, for e.g. LDH-1 has the highest mobility towards the anode and LDH-5 is the slowest.

Isoenzymes have different tissue distributions. Therefore the pattern of isoenzymes found in the plasma may serve as a means of identifying the site of tissue damage. Example of the diagnostic use of isoenzymes are the study of Lactate Dehydrogenase and Creatine Kinase.

Q. 2

True about isoenzymes is/are:

A

Different km value

B

Act on different substrate

C

Same electrophoretic mobility

D

All

Q. 2

True about isoenzymes is/are:

A

Different km value

B

Act on different substrate

C

Same electrophoretic mobility

D

All

Ans.

A

Explanation:

Isozymes are the physically distinct forms of the same enzymes that catalyze the same reaction, and differ from each other structurally, electrophoretically and immunologically.

They differ in their physical properties because of genetically determined difference in amino acid sequence.

They are separated by electrophoresis as they have different electrophoretic mobility.

They have different Km value.

Isoenzyme of an oligomeric enzyme process differ in combination of its peptide protomer.

Q. 3

Which isoenzyme of LDH is seen in heart

A

LDH 1

B

LDH 2

C

LDH 3

D

LDH 4

Q. 3

Which isoenzyme of LDH is seen in heart

A

LDH 1

B

LDH 2

C

LDH 3

D

LDH 4

Ans.

A

Explanation:

Ans. is ‘a’ i.e., LDH1

Q. 4

First enzyme to be raised in MI is ‑

A

CPK-MB

B

LDH

C

Myoglobin

D

Troponin-I

Q. 4

First enzyme to be raised in MI is ‑

A

CPK-MB

B

LDH

C

Myoglobin

D

Troponin-I

Ans.

C

Explanation:

Ans. is ‘c’ i.e., Myoglobin

Q. 5

Enzyme specificity is given by ‑

A

Km

B

Vrm„

C

Both

D

None

Q. 5

Enzyme specificity is given by ‑

A

Km

B

Vrm„

C

Both

D

None

Ans.

A

Explanation:

Ans. is ‘a’ i.e., K.

The Km of an enzyme is the concentration of the substrate that enables the enzyme to function at half maximum activity and is therefore a measure of the specificity of a substrate.for the enzyme” Clinical biochemistry

Actually enzyme specificity is not measured by Km alone.

It is measured by the ratio Kcat/Km which is a second order rate constant for the reaction between substrate and free enzyme.

This ratio is important, for it provides a direct measure of enzyme efficiency and specificity.

Note : Kcat is turnover number and measures the rate of the catalytic process.

Q. 6

Q10 in enzyme matches with ‑

A

2

B

4

C

8

D

10

Q. 6

Q10 in enzyme matches with ‑

A

2

B

4

C

8

D

10

Ans.

A

Explanation:

Ans. is ‘a’ i.e., 2

Most enzyme show a 50-300% (average 200%) increase in reaction rate when the temperature is increased by 10°, and the ratio of rate constant at two temperatures 10° apart is usually between 1.5 to 4 (average 2) for most enzymes.

This value is termed as Q10.

“The rate of enzymatic reaction doubles with every 10° rise in temperature. “

Q. 7

Fastest acting enzyme ‑

A

LDH

B

Trypsin

C

Catalase

D

None

Q. 7

Fastest acting enzyme ‑

A

LDH

B

Trypsin

C

Catalase

D

None

Ans.

C

Explanation:

Ans. is ‘c’ i.e., Catalase

Measurement of enzyme activity

The activity of enzyme is measured in terms of the following :

Unit of enzyme activity : – By international agreement, one unit enzyme activity is defined as the amount causing transformation of 1.0 micro mole of substrate per minute at 25° C. It is usually expressed as mole of substrate disappeared or mole of product formed per minute.

Specific activity : – It refers to the number of enzyme units per milligram of protein. It is a measure of enzyme purity; higher the enzyme purity, more is the specific activity.

Turn over number : – This refers to the number of substrate molecules transformed per unit time by a single enzyme molecule (or by a single catalytic site), when the enzyme concentration alone is rate-limiting factor. Catalase has the highest turnover number and hence is the fastest active enzyme. Carbonic anydrase has the 2″ fastest turnover number; therefore, it is 2nd fastest active enzyme (after catalase). Lysozyme has the lowest turnover number and therefore is slowest acting.